In rotor spinning of yarn using an open-end spinner, fibers which have first been separated into individual fibers by a combing or fiber opening mechanism and then drawn under the influence of a flowing air stream into the spinning chamber of the rotor, are collected within the peripherally extending fiber-collecting groove, formed along the maximum diameter region within the spinning chamber. The fibers thus deposited in the fiber-collecting groove are withdrawn continuously therefrom in the form of a twisted and elongated strand of yarn through the yarn guide tube. The rotor, which rotates at an extremely high speed, is conventionally made of an aluminium alloy having a relatively low specific gravity and moderate strength with a view to reducing power consumption in driving the rotor and to avoid damage or deformation of the rotor by the high centrifugal forces developed by the rotor as it is being driven at high speed.
However, the demand for improvement in open-end spinning productivity has boosted the rotor speed up to more than 30,000 rpm, with the result that the rotor of aluminium alloy used for a certain period of service has shown deformation or wear at the inner peripheral surface or fiber contacting surface along which the fibers are forced to slide during their introduction into the rotor under the influence of the centrifugal force, as well as at the fiber collecting groove formed at the maximum diameter in the spinning chamber of the rotor. Such wear is particularly rapid at the latter fiber collecting groove where the fibers are collected and then formed into a strand of yarn while being twisted. Thus, said fiber collecting groove is placed under continuous abrasive action by the fibers. Since the configuration of the fiber collecting groove plays a critical part in the formation of a yarn, any wear or deformation thereat is harmful and will naturally affect the process of yarn formation. As a result, the quality of the yarn being spun will be degraded.
There are several factors which are responsible for the above-stated wear of the rotor. One is the magnitude of impacting shocks which take place when the individual fibers flowing out of the fiber feeding tube impinge against the rotor's inner fiber contacting surface which is moving at a much greater peripheral speed than the fibers. Another is the abrasive action produced when such fibers are forced to slide in contact with the inner peripheral surface toward the fiber collecting groove under the influence of the centrifugal force developed by the rotor running at an extremely high speed. In addition to such impinging fibers, foreign matter or impurities contained in the fibers, such as grit, fragments of leaves or seeds, etc. promote rapid wear at the interior surfaces of the rotor. Furthermore, the fiber-collecting groove, where the fibers are twisted with each other to form a yarn under the influence of great centrifugal force and are subsequently withdrawn therefrom inwardly, against that centrifugal force, is subjected to an extremely high degree of continuous abrasive, frictional contact with the twisting yarn. Consequently, inordinate wear with consequent deformation of the groove configuration will take place after a period of spinning operation, thus deteriorating the quality of yarn which is spun out.
Many attempts were made to provide an improved aluminium rotor which could successfully withstand both high-speed operation and the above-mentioned abrasive forces for a sufficiently extended period of service, including surface treatment processes such as by coating, electro-plating or anodizing. Of these, anodizing of the rotor proved to be the best, because it exhibited the desired wear-resisting performance, thus retaining the originally machined flat surfaces of the fiber collecting groove and of the fiber contacting surface and causing the least change in the internal diameters of the rotor.
In recent years, under the demand for further increases of rotor speed up to from about 60,000 to 100,000 rpm for achieving still higher producitivity in spinning mills, the conventional rotor of aluminium alloy having anodized surfaces has been found inadequate for meeting the exacting requirements of rotor spinning at such super high speeds.
An approach to solving the problems associated with such conventional rotors has been proposed by U.S. Pat. No. 4,167,846, according to which the rotor body is made of steel and its interior surfaces are hardened by such treatment as induction heating, carburizing or nitriding. The surfaces obtained on the rotor by the method according to this prior art can offer adequate wear-resistance even at rotor speeds as high as 60,000 to 80,000 rpm. However, a rotor which has undergone such case hardening treatment has a disadvantage in that the heating necessary for the treatment is applied not only to the area which calls for hardening, but also to other portions in the rotor. As a result of such heating, strain or distortion will inevitably be produced within the rotor, causing harmful vibrations during the rotation thereof at a very high speed, thereby inviting degradation of yarn quality and rendering the rotor incapable of providing stable operation over a prolonged period of useful service.